Add form support for fields which can only use bindings rather than explicit onchange handlers

packages/standard-components/src/forms/AttachmentField.svelte

@@ -1,27 +1,28 @@
 <script>
   import SpectrumField from "./SpectrumField.svelte"
   import Dropzone from "../attachments/Dropzone.svelte"
+  import { onMount } from "svelte"
 
   export let field
   export let label
 
-  let previousFiles = []
-  let files = []
-  $: {
-    // Only actually update the value when it changes, so that we don't trigger
-    // validation unnecessarily
-    if (files !== previousFiles) {
-      fieldApi?.setValue(files)
-      previousFiles = files
-    }
-  }
-
   let fieldState
   let fieldApi
+
+  // Update form value from bound value after we've mounted
+  let value
+  let mounted = false
+  $: mounted && fieldApi?.setValue(value)
+
+  // Get the fields initial value after initialising
+  onMount(() => {
+    value = $fieldState?.value
+    mounted = true
+  })
 </script>
 
-<SpectrumField {label} {field} bind:fieldState bind:fieldApi>
+<SpectrumField {label} {field} bind:fieldState bind:fieldApi defaultValue={[]}>
-  {#if fieldState}
+  {#if mounted}
-    <Dropzone bind:files />
+    <Dropzone bind:files={value} />
   {/if}
 </SpectrumField>

packages/standard-components/src/forms/BooleanField.svelte

@@ -13,18 +13,19 @@
   const onChange = event => {
     fieldApi.setValue(event.target.checked)
   }
-
-  // Ensure a valid boolean value is set
-  onMount(() => {
-    fieldApi.setValue($fieldState.value || false)
-  })
 </script>
 
-<SpectrumField {label} {field} bind:fieldState bind:fieldApi>
+<SpectrumField
+  {label}
+  {field}
+  bind:fieldState
+  bind:fieldApi
+  defaultValue={false}>
   {#if fieldState}
     <div class="spectrum-FieldGroup spectrum-FieldGroup--horizontal">
       <label class="spectrum-Checkbox" class:is-invalid={!$fieldState.valid}>
         <input
+          checked={$fieldState.value}
           on:change={onChange}
           type="checkbox"
           class="spectrum-Checkbox-input"

packages/standard-components/src/forms/Form.svelte

@@ -34,7 +34,7 @@
 
   // Form API contains functions to control the form
   const formApi = {
-    registerField: field => {
+    registerField: (field, defaultValue = null) => {
       if (!field) {
         return
       }
@@ -47,8 +47,8 @@
       const validate = createValidatorFromConstraints(constraints, field, table)
 
       fieldMap[field] = {
-        fieldState: makeFieldState(field),
+        fieldState: makeFieldState(field, defaultValue),
-        fieldApi: makeFieldApi(field, validate),
+        fieldApi: makeFieldApi(field, defaultValue, validate),
         fieldSchema: schema?.[field] ?? {},
       }
       fieldMap = fieldMap
@@ -60,13 +60,16 @@
   setContext("form", { formApi, formState })
 
   // Creates an API for a specific field
-  const makeFieldApi = (field, validate) => {
+  const makeFieldApi = (field, defaultValue, validate) => {
     return {
       setValue: value => {
         const { fieldState } = fieldMap[field]
         fieldState.update(state => {
-          state.value = value
+          if (state.value === value) {
-          state.error = validate ? validate(value) : null
+            return state
+          }
+          state.value = value == null ? defaultValue : value
+          state.error = validate ? validate(state.value) : null
           state.valid = !state.error
           return state
         })
@@ -76,13 +79,13 @@
   }
 
   // Creates observable state data about a specific field
-  const makeFieldState = field => {
+  const makeFieldState = (field, defaultValue) => {
     return writable({
       field,
       fieldId: `${Math.random()
         .toString(32)
         .substr(2)}/${field}`,
-      value: initialValues[field] ?? null,
+      value: initialValues[field] ?? defaultValue,
       error: null,
       valid: true,
     })

packages/standard-components/src/forms/LongFormField.svelte

@@ -1,4 +1,5 @@
 <script>
+  import { onMount } from "svelte"
   import { RichText } from "@budibase/bbui"
   import SpectrumField from "./SpectrumField.svelte"
 
@@ -8,17 +9,17 @@
 
   let fieldState
   let fieldApi
-  let previousValue = ""
-  let value = ""
 
-  $: {
+  // Update form value from bound value after we've mounted
-    // Only actually update the value when it changes, so that we don't trigger
+  let value
-    // validation unnecessarily
+  let mounted = false
-    if (value !== previousValue) {
+  $: mounted && fieldApi?.setValue(value)
-      fieldApi?.setValue(value)
+
-      previousValue = value
+  // Get the fields initial value after initialising
-    }
+  onMount(() => {
-  }
+    value = $fieldState?.value
+    mounted = true
+  })
 
   // Options for rich text component
   const options = {
@@ -37,8 +38,8 @@
   }
 </script>
 
-<SpectrumField {label} {field} bind:fieldState bind:fieldApi>
+<SpectrumField {label} {field} bind:fieldState bind:fieldApi defaultValue="">
-  {#if fieldState}
+  {#if mounted}
     <div>
       <RichText bind:value {options} />
     </div>

packages/standard-components/src/forms/SpectrumField.svelte

@@ -8,6 +8,7 @@
   export let fieldState
   export let fieldApi
   export let fieldSchema
+  export let defaultValue
 
   // Get contexts
   const formContext = getContext("form")
@@ -16,16 +17,14 @@
   const component = getContext("component")
 
   // Register field with form
-  $: formApi = formContext?.formApi
+  const formApi = formContext?.formApi
-  $: labelPosition = fieldGroupContext?.labelPosition || "above"
+  const labelPosition = fieldGroupContext?.labelPosition || "above"
-  $: formField = formApi?.registerField(field)
+  const formField = formApi?.registerField(field, defaultValue)
 
   // Expose field properties to parent component
-  $: {
+  fieldState = formField?.fieldState
-    fieldState = formField?.fieldState
+  fieldApi = formField?.fieldApi
-    fieldApi = formField?.fieldApi
+  fieldSchema = formField?.fieldSchema
-    fieldSchema = formField?.fieldSchema
-  }
 
   // Extract label position from field group context
   $: labelPositionClass =